From the internet…(I had no clue either)
An old term from the Southwest that refers to a gun that is not worn daily. It won't have the scratches, wear marks, etc a daily wear gun would have. These guns were not something that were never used or "useless." In the time the term came about they were functional guns (sometimes, heavily modified for better accuracy/reliability/etc) that might have some custom engraving, polishing, or custom grips. They didn't make many guns purely for show - they made guns to use and users modified them for show. They were normally worn in tooled leather holsters as opposed to daily wear holsters - which were plain.